DESCRIPTION: (Applicant's Abstract) The proposed project, entitled the "Longitudinal Study of AIDS Risk among Drug Users," is designed to understand a set of interrelated critical issues in AIDS prevention among out-of-treatment injection drug users (IDUs) and crack cocaine users (CCUs). Building on the Hartford NIDA Cooperative Agreement (#DA07284), this study will re-recruit the COPE II cohort (N=1300) of IDUs and CCUs to achieve the following specific aims: 1) to assess individual, perceived peer, and social context factors associated with sustained HIV risk reduction over time, sustained HIV risk despite targeted intervention, and relapse into high risk following a period of risk reduction; 2) to assess the impact of a theory driven harm reduction booster intervention against a comparison 'placebo' general health education track in promoting longer term HIV risk reduction in this cohort; 3) to examine the pattering of HIV risk and drug use over time associated with life event/life change antecedents not specifically related to formal risk reduction intervention; and 4) to assess individual, perceived peer, and social context factors associated with attrition and/or continued participation in intervention and data collection. The first two of these aims structure the proposed study, while the latter two are addressed through nested substudies using selected subsamples of the larger cohort. Two waves of data collection were completed with the cohort in the Cooperative Agreement. In the proposed follow-up study, intensive outreach will seek to relocate all cohort participants to conduct two additional follow-up interview waves (at relocation and four months later) using both the Risk Behavior Follow-up Assessment and a special trailer designed to assess hypothesized factors in sustained risk reduction, sustained high risk, relapse to high risk, and attrition. We anticipate that intensive outreach will relocate 70% of the cohort for the third wave of data collection (n=925), and 80% of these for the fourth wave (n=740). Analyses will include refinement of operational definitions of high and low HIV risk categories essential for the characterization of sustained high risk reduction, sustained low risk, and risk relapse; examination of individual risk behaviors as well as scores on aggregate risk-behavior scales at the third and fourth waves of data collection; transition modeling of behavior change at multiple and varying points in time; and analysis of attrition as an outcome and as a potential source of analytical bias. These methods will be used to track risk reduction behavior changes over time and to compare long-term efficacy of AIDS prevention intervention for this high-risk drug using population.